System and method for generating and controlling conducted acoustic waves for geophysical exploration

ABSTRACT

An improved system and method for generating and controlling conducted acoustic waves for geophysical exploration are provided. A plurality of overpressure waves are generated by at least one overpressure wave generator comprising at least one detonation tube having an open end. The at least one overpressure wave generator is oriented so the plurality of overpressure waves are not directed directly towards a target media. The recoil force of the at least one overpressure wave generator occurring during generation of the plurality of overpressure waves is coupled to the target media to generate conducted acoustic waves. The timing of the generation of the plurality of overpressure waves can be in accordance with a timing code and can be used to steer the conducted acoustic waves to a location of interest in the target media.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application60/792,420, filed Apr. 17, 2006, and U.S. Provisional Patent Application60/850,685, filed Oct. 10, 2006, both of which are incorporated hereinby reference. This application is also related to a U.S. ProvisionalPatent Application filed concurrently on Oct. 10, 2006, titled “A Systemand Method for Generating and Directing Very Loud Sounds”.

FIELD OF THE INVENTION

The present invention relates generally to a system and method forgenerating and controlling an overpressure wave. More particularly, thepresent invention relates to controlling the detonation of afuel-oxidant mixture flowing within a tubular structure to generate,steer and focus an overpressure wave. The present invention also relatesto a system and method for coupling the recoil force, namely, thebackward or reactive force produced by the generation of theoverpressure wave, to a target media in order to produce a conductedacoustic wave that can be used to explore or otherwise characterize aregion of interest within the target media. More particularly, thepresent invention also relates to controlling the recoil force caused bythe detonation of a fuel-oxidant mixture flowing within one or moretubular structures to generate and control conducted acoustic waves forgeophysical exploration purposes.

BACKGROUND OF THE INVENTION

An overpressure wave is a transient air pressure, such as the blast wavefrom an explosion, which is greater than the surrounding atmosphericpressure. Such overpressure waves originate at the point of detonationof the explosion and typically propagate outward from the point ofdetonation in all directions. Such explosions may also involve therelease of intense heat.

Various methods are often employed to cause an overpressure wave to bedirected in a desired direction. For example, directed charge methodsmight involve placement of an explosive against an object capable ofsustaining the blast (e.g., a thick concrete structure) so that theenergy of the explosion will be directed outward from the object.Similarly, various methods of ‘shaped charges’ are used to cause themajority of the energy of an explosion to be directed in a desireddirection. Similarly, blast barriers such as concrete walls or earthenberms are often used to redirect the energy of potential explosions awayfrom valuable assets such as buildings. Great Britain patent GB1,269,123 describes detonation of ethylene and oxygen in combustiontubes and use of the detonation wave for coating, to drive a turbineengine, and for rocket propulsion. U.S. Pat. Nos. 4,662,844 and4,664,631 describe igniting fuel and oxidizer mixtures within combustionchambers to produce a detonative combustion wave to simulate weaponseffects. U.S. Pat. No. 5,864,517 describes a pulsed combustion acousticwave generator to produce acoustic waves that can be used for non-lethalincapacitation, impairment, or immobilization for crowd control or selfdefense; mine detonation; wildlife control; acoustic cleaning; andtriggering avalanches. These methods are similar in that they cause anoverpressure wave to be directed out of the open end of a detonationtube. As such, various methods exist for directing overpressure waves.

It is desirable, however, to have an improved system and method forgenerating and controlling overpressure waves for useful purposes.

Seismic shock waves introduced into the ground are often used ingeophysical exploration systems. Such seismic shock waves are typicallyintroduced, or conducted, into the ground using either explosives or avibration coupler. The use of explosives for such purposes is dangerous,expensive, and the resulting blast is difficult to control precisely.The transportion of a vibration coupler typically requires a 5- or10-ton truck and it is time-consuming to set up.

Great Britain Patent 934,749 discloses an acoustical generator andseismic exploring system where an open ended combustion chamber is usedto generate acoustic energy pulses that are directed downward into wateror at the ground and a seismic detector is used to detect reflections ofthe pulses for seismic surveying.

U.S. Pat. Nos. 3,235,026 and 4,043,420 describe closed detonationchambers attached to the ground via bottom plates where a detonation ofa oxygen-fuel-oxidant mixture produces a shock wave that applies acompressive inpulse against each bottom plate and the surface of theearth on which it rests thus initiating a seismic wave into thesubsurface. The patents disclose alternative forms of shock absorbersthat cause an opening in the detonation chambers to vent exhaust fumes.

U.S. Pat. No. 5,864,517 states “by introducing sound waves into theground and recording their reflections, scientists can determine thecomposition of the earth's sublayers” and that a pulsed combustionacoustic wave generator “could generate precise sound waves at exactintervals to increase the amount of information that could be gained”from geophysical exploration studies. This prior art however does notteach how such precise sound waves at exact intervals can be generated.

An alternative geophysical exploration approach invented by the presentinventor and described in U.S. Pat. No. 6,360,173 uses a detonation tubeas an impulsive seismic source to generate a sequence of time-codedmonocycle waveforms that propagate to geophysical structures and/orproperties causing the geophysical structures and/or properties toreturn echoes, and a sensing means for sensing data that arerepresentative of the echoes.

It is desirable to have an improved system and method for introducingenergy into the ground or another media for exploration purposes.

SUMMARY OF THE INVENTION

Briefly, the present invention is an improved system and method forgenerating overpressure waves having a desired magnitude. A fuel-oxidantmixture having desired combustion characteristics is introduced at adesired flow rate into a tubular structure. In one exemplary embodiment,the tubular structure comprises a detonation tube having a specifiedlength and diameter. The flowing fuel-oxidant mixture is detonated atone end of the detonation tube by introducing a spark within the flowingfuel-oxidant mixture. A resulting detonation impulse travels the lengthof the detonation tube as it ignites the flowing fuel-oxidant mixtureremaining within it. The combustion characteristics and the flow rate ofthe fuel-oxidant mixture can be selected to control the energy of thedetonation impulse. One or more additional detonation tubes havinggraduated (i.e., larger and larger) diameters can be optionally combinedwith the initial detonation tube to create a graduated detonation tubecombination causing the detonation impulse to be amplified as it travelsthrough each successive detonation tube having a larger diameter

Under a first exemplary embodiment of the invention, the detonation tube(or graduated detonation tube combination) has an open end from which anoverpressure wave is projected in a desired direction. Under onearrangement, multiple detonation tubes (or graduated detonation tubecombinations) are co-located and grouped in one of various possibleconfigurations causing their projected overpressure waves to becombined. The value of the combined projected overpressure waves isequal to the number of detonation tubes, N, times the overpressureprojected by a single detonation tube. The far-field combined power ofthe combined projected overpressure waves is N² times the powerprojected from a single detonation tube. Under an alternativearrangement, multiple individual detonation tubes (or graduateddetonation tube combinations) are located in a sparse array allowing thetiming of the detonations within the various detonation tubes to becontrolled such that the projected overpressure waves are steered sotheir power combines at a desired location(s). As such, the one or moredetonation tubes can be used to focus and steer the overpressure wavesto produce a desired power at a desired location. Applications of thefirst exemplary embodiment of the invention include but are not limitedto explosives emulation for training purposes, explosives barriertesting, demolition of mines/buildings, crowd control, border defense,animal/bird/insect control, prisoner control, structuralstrength/integrity testing, providing rotary motion to a windmill or aturbine, use as a thrust source for rocket-like propulsion,dirt/sand/snow/ice removal for roads/runways/airplanes/etc,fruit/vegetable/grain/etc. harvesting from trees/bushes/plants andcomparable agriculture applications, industrial cleaning (e.g., smokestacks/precipitators), object forming (e.g., a compliant press/moldingprocess), fire suppression, and, in general, most any areadenial/security application.

Under a second exemplary embodiment of the invention, the recoil forcecaused by each of a timed sequence of generated overpressure waves iscoupled to a target media such as the ground, ice, or water in order toproduce a sequence of conducted acoustic waves that can be used toexplore a region of interest within the target media, for example, anoil deposit within the ground. Under one exemplary arrangement, therecoil force of the generated overpressure waves is coupled to thetarget media by a coupling component. In one embodiment, the recoilforce is equal to the derivative of the backward momentum resulting fromthe generated overpressure waves. Under an alternative exemplaryarrangement, the overpressure wave generator couples the recoil force ofthe generated overpressure waves directly to the target media. Thesequence of conducted acoustic waves travel through the target media,reflect from the region of interest, and the corresponding reflectionsare received by each of a plurality of receiving devices arranged in anarray. The received reflections can be processed in order to produce athree-dimensional data set characterizing the region of interest. Withthis embodiment, the overpressure wave may optionally be coupled into amuffling apparatus that muffles the sound associated with theoverpressure wave and also damps the overpressure wave prior to itsrelease into the surrounding environment. The coupling component of thisembodiment comprises a spring-like mechanism that has damping controlwhere the shape and material of the coupling component is selected toachieve an appropriate balance between energy transformation and adverseimpact to the system (i.e., wear). The coupling component includes animpedance plate having a desired shape, or footprint, which is in directcontact with the surface of the target media. The impedance platecouples the recoil force to the target media producing a conductedacoustic wave. As with the first exemplary embodiment, under onearrangement, multiple detonation tubes (or graduated detonation tubecombinations) are co-located and grouped in one of various possibleconfigurations causing their projected overpressure waves to be combinedas previously described above, which provides for a correspondingincrease in the recoil force available to be coupled to the targetmedia. Under an exemplary alternative arrangement, multiple individualdetonation tubes (or graduated detonation tube combinations) are locatedin a sparse array allowing the timing of the detonations within thevarious detonation tubes to be controlled. With this approach, thetiming of conducted acoustic waves is controlled to focus and steer themso as to combine at a desired location within the target media.Applications of the second embodiment of the invention include but arenot limited to powering an engine or a pump, driving in fenceposts/piles into the ground, use as a tamping device (e.g., to compactdirt), use as a forced entry device (like a battering ram), imaging awater body bottom, and use to crush/deform objects/stamp metal/etc.

Under a third exemplary embodiment of the invention, the overpressurewave generator of the present invention is used to generate a shearwave. Under one arrangement, an overpressure wave generator is orientedparallel to the target media and used to produce overpressure waves. Itsrecoil force is used to generate a plane shear wave. Under analternative arrangement, two or more overpressure wave generators areoriented parallel to a target media and arranged such that they directoverpressure waves in opposite directions so that their recoil force canbe used to generate a spherical shear wave.

The present invention provides a method for generating a conductedacoustic wave, comprising the steps of causing at least one detonationwithin at least one detonation tube having an open end to generate atleast one overpressure wave and coupling a recoil force of the at leastone overpressure wave to a target media to generate at least one saidconducted acoustic wave. Under one arrangement, the open end of the atleast one detonation tube is oriented to direct the overpressure wavesperpendicular to and away from the target media. Under anotherarrangement, the open end of the at least one detonation tube isoriented to direct the overpressure waves parallel to the target mediacausing the recoil force to produce either a plane shear wave or aspherical shear wave depending on the how the at least one overpressurewave generator is arranged.

The target media can be any one of ground, ice, or water. Theoverpressure waves can be generated by controlling the detonation of afuel-oxidant mixture flowing within each of said at least one detonationtube. The overpressure waves can be generated in accordance with adetonation parameter, which could be a timing code such as a Barkercode. The sound of the at least one overpressure wave can be muffled.

The acoustic waves can also be directed to a location of interest withinthe target media by controlling the relative timing of the generation ofthe overpressure waves.

The present invention provides a system for generating a conductedacoustic wave, comprising at least one detonation tube having an openend for generating at least one overpressure wave and a couplingcomponent for coupling a recoil force of said at least one overpressurewave to a target media to generate at least one said conducted acousticwave. The system may further comprise a stabilizing mechanism thatprovides stability to the movement of the at least one detonation tube.

With one approach, the open end of the at least one detonation tube isoriented to direct the at least one overpressure wave perpendicular toand away from the target media where the stabilizing mechanism allowsonly up and down movement. Alternatively, the open end of the at leastone detonation tube is oriented to direct the at least one overpressurewave parallel to the target media where the stabilizing mechanism allowsonly side to side movement.

Each of the overpressure waves is generated by controlling thedetonation of a fuel-oxidant mixture flowing within each of said atleast one detonation tube. The overpressure waves can be generated inaccordance with detonation parameters, which could be a timing code suchas a Barker code.

A muffler may be associated with at least one detonation tube.

The invention provides a system for generating and directing conductedacoustic waves, comprising a plurality of overpressure wave generatorspositioned in a sparse array, each of the plurality of overpressure wavegenerators comprising at least one detonation tube having an open endand being used to generate a plurality of overpressure waves, each ofthe plurality of overpressure waves having a recoil force; and aplurality of coupling components for coupling the recoil forces of saidplurality of overpressure waves to a target media to generate saidconducted acoustic waves, the conducted acoustic waves being directed toa location of interest within the target media based upon the relativetiming of the generation of the plurality of overpressure waves.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingdrawings. In the drawings, like reference numbers indicate identical orfunctionally similar elements. Additionally, the left-most digit(s) of areference number identifies the drawing in which the reference numberfirst appears.

FIG. 1A illustrates an exemplary prior art detonation tube havingseparate fuel and oxidizer supplies and a spark plug that ignites thefuel-oxidant mixture at the closed end of the tube after the tube hasbeen filled;

FIG. 1B illustrates a second exemplary prior art detonation tube havinga fuel-oxidant mixture supply and a spark plug that ignites thefuel-oxidant mixture at the closed end of the tube after the tube hasbeen filled;

FIG. 2A illustrates an exemplary detonation tube of the presentinvention having a detonator that receives a fuel-oxidant mixture from afuel-oxidant mixture supply and ignites the fuel-oxidant mixture as itis flowing into the tube;

FIG. 2B depicts a first embodiment of the detonator of the presentinvention that functions by creating an electrical arc within a streamof a gas mixture

FIG. 2C depicts a second embodiment of the detonator of the presentinvention is similar to that depicted in FIG. 2B except it includes twoconductors that diverge into the main tube causing the length of thespark to increase as it travels into the main detonation tube;

FIG. 3A depicts an end view of another embodiment of the detonator ofthe present invention.

FIG. 3B depicts a side view of the detonator of FIG. 3A.

FIG. 4 depicts an exemplary graduating detonation tube combinationwhereby larger and larger diameter tubes are used in combination toamplify a detonation wave;

FIG. 5 depicts an exemplary detonation tube having a diameter thatincreases across the length of the tube that amplifies a detonationwave;

FIG. 6 illustrates a tube having a gradually shrinking and thengradually enlarging tube circumference;

FIG. 7A depicts a first detonation tube alongside a second detonationtube;

FIG. 7B depicts four detonation tube combinations arranged such that thelarger detonations tubes of the detonation tube combinations are incontact with each other;

FIG. 7C depicts three enlarging diameter detonation tubes;

FIG. 7D depicts seven detonation tubes arranged to resemble a hexagonalstructure;

FIG. 7E depicts twelve detonation tubes arranged in a circular manner;

FIG. 8 depicts a side view of three detonation tubes having a firstdiameter connected to a larger detonation tube having a second largerdiameter to amplify the combined pulse generated by the smaller tubes;

FIG. 9 provides an illustration of how the timing of the firing ofindividual detonation tubes focuses the power at a single point in thefar field;

FIG. 10 depicts a sparse array of 4 detonation tubes being detonated soas to steer the overpressure waves such that they combine at a desiredlocation;

FIG. 11 depicts a sparse array of 4 groups of detonation tubes beingdetonated so as to steer the overpressure waves such that they combineat a desired location;

FIG. 12 illustrates an example of efficient packing of hexagonalsub-arrays of 7 detonation tubes into a combined array totaling 224detonation tubes;

FIG. 13 depicts a system that harnesses the recoil force of theoverpressure wave generator of the present invention for seismicexploration;

FIG. 14 depicts the logical flow diagram for seismic explorationprocess;

FIG. 15 depicts an array of seismic exploration systems of the presentinvention;

FIG. 16 depicts a top down view of a scalable circular array pattern ofseismic exploration systems of the present invention;

FIG. 17A depicts a side view of a plane shear wave generator inaccordance with one embodiment of the present invention;

FIG. 17B depicts a plane shear wave;

FIG. 18A depicts a plan view of a spherical shear wave generator inaccordance with one embodiment of the present invention;

FIG. 18B depicts a spherical shear wave; FIG. 18C depicts a plan view ofa spherical shear wave generator in accordance with another embodimentof the present invention; and

FIG. 18D depicts a plan view of a spherical shear wave generator inaccordance with still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully in detail withreference to the accompanying drawings, in which the exemplaryembodiments of the invention are shown. This invention should not,however, be construed as limited to the embodiments set forth herein;rather, they are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

The present invention provides an improved system and method forgenerating and controlling an overpressure wave, which is also bereferred to herein as a sound wave or sound pulse. Exemplaryoverpressure waves can be characterized by their frequency in the rangeof 0.1 Hz to 30 KHz. The basis of the system is the ignition of a highenergy, detonable gaseous or dispersed fuel-air or fuel-oxygen mixturewithin a tube that is open at one end, where any of a number offlammable fuels can be used including ethane, methane, propane,hydrogen, butane, alcohol, acetylene, MAPP gas, gasoline, and aviationfuel. The gas mixture is detonated at the closed end of the tube causinga detonation wave to propagate the length of the tube where detonationends and the detonation wave exits the open end of the tube as anoverpressure wave. The tube is referred to herein as a detonation tubeand the detonation wave is referred to herein as a detonation pulse orimpulse.

One embodiment of the present invention comprises at least onedetonation tube apparatus and a timing control mechanism for controllingthe timing of detonations. The detonation tube apparatus comprises atleast one detonation tube, at least one detonator, and a fuel-oxidantmixture supply subsystem. One or more detonators can be used with agiven detonation tube and a detonator can be used with multipledetonation tubes. Associated with the one or more detonators is one ormore spark initiators where a single spark initiator may initiate sparksin multiple detonators, which may be in parallel or in series, andmultiple spark initiators may initiate sparks in a single detonator. Thetiming control mechanism controls the timing of the one or more sparkinitiators.

The spark initiator may be a high voltage pulse source. As analternative to the high voltage pulse source a triggered spark gapapproach can be used a spark initiator. Other alternatives for a sparkinitiator include a laser and an exploding wire.

The timing control mechanism can be a simple trigger mechanism, fixedlogic, or be a more complex control processor. A control processor mayalso be used to control variable parameters of the fuel-oxidant mixturesupply subsystem or such parameters may be fixed.

The fuel-oxidant mixture supply subsystem maintains a desired mass ratioof fuel versus oxidant of the fuel-oxidant mixture and a desired flowrate of the fuel-oxidant mixture. Desired fuel versus oxidant ratio andflow rate can be selected to achieve desired detonation characteristicsthat depend on length and diameter characteristics of the detonator. Forexample, one embodiment uses a propane-air fuel-oxidant mixture, a massratio of 5.5 and a flow rate of 50 liters/minute for a detonator havinga length of 1″ and a ¼″ diameter and made of Teflon, a first detonationtube made of stainless steel having a length of 9″ and a diameter thattapers from 0.8″ at the end connected to the detonator to 0.65″ at theend connected to a second detonation tube made of titanium having alength of 32″ and a 3″ diameter. Alternatively, the first detonationtube may have a constant diameter of 0.8″.

Commercially available mass flow control valve technology can be used tocontrol the mass ratio of fuel versus oxidant of the fuel-oxidantmixture and the flow rate of the fuel-oxidant mixture. Alternatively,commercially available technology can be used to measure the mass flowof oxidant into a fuel-oxidant mixture mixing apparatus and the preciseoxidant mass flow measurement can be used to control a mass flow valveto regulate the mass flow of the fuel needed to achieve a desired massratio of fuel versus oxidant of the fuel-oxidant mixture.

Detonation within Flowing Fuel-Oxidant Mixture

Prior art gas detonation systems either required long tubes or highlydetonable gas mixtures such as oxygen and hydrogen in order to produce adetonation. Otherwise they will only “deflagrate” which is a slow andnearly silent process. In contrast, one aspect of the present inventionprovides the ability to produce short, high intensity sound pulseswithin a tube as short as one foot long and 2 inches diameter, usingonly moderately explosive gas mixtures such as propane and air. Unlikethe prior art systems, this aspect of the present invention is embodiedin an exemplary system that passes an electric arc through a flowing (ormoving) stream of gas and oxidizer mixture that is filling the tubewithin which the detonation will take place. When the tube issubstantially full, a fast spark is initiated within the flowing gas atthe filling point in the tube, which triggers the subsequent detonationof all the gas inside the tube. Alternatively, the flowing gas can bedetonated by a laser or by any other suitable ignition and detonationmethod according to the present invention. This ignition within flowinggas technique dramatically shortens the tube length required to producea detonation when compared to prior art systems that ignited non-flowingor otherwise still gas mixtures. Moreover, detonation according to thisaspect of the present invention requires on the order of 1 Joule ofenergy to detonate the fuel-oxidant mixture whereas prior art systemsmay require 100's to 1000's of Joules of energy to achieve detonation.Further desirable results of this method are the reduction ofuncertainty of time between the electric arc trigger and the subsequentemission of the sound pulse from the tube and the repeatability ofdetonation pulse magnitude. As such, the detonator according to thisaspect of the present invention enables precise timing and magnitudecontrol of an overpressure wave.

FIG. 1A depicts a side view of a prior art detonation system. Adetonation tube 100 has separate fuel supply 102 and oxidizer supply 104which are opened during a fill period to fill detonation tube 100 withfuel-oxidant mixture 106. After the fill period, fuel supply 102 andoxidizer supply 104 are closed and at a desired time a charge is appliedthrough high voltage wire 108 to spark plug 110, which ignites thefuel-oxidant mixture 106 causing a detonation wave to propagate down thelength of the detonation tube 100 and exit its open end 112. Similarly,FIG. 1B depicts a side view of another prior art detonation system wheredetonation tube 100 has a fuel-oxidant mixture supply 105 which isopened during a fill period to fill detonation tube 100 withfuel-oxidant mixture 106. After the fill period, fuel-oxidant mixturesupply 105 is closed and at a desired time a charge is applied throughhigh voltage wire 108 to spark plug 110, which ignites the fuel-oxidantmixture 106 causing a detonation wave to propagate down the length ofthe detonation tube 100 and exit its open end 112.

FIG. 2A depicts the detonation tube 100 of the overpressure wavegenerator 11 of the present invention being supplied by fuel-oxidantmixture supply 105 via detonator 114, where a spark ignites within thefuel-oxidant mixture 106 while the detonation tube 100 is being filedwith the fuel-oxidant mixture 106 causing a detonation wave to propagatedown the length of the detonation tube 100 and exit its open end 112. Inone embodiment, an appropriate fuel-oxidant mixture flow rate ismaintained during ignition within the flowing fuel-oxidant mixture. Ithas been found that over a substantial range of flows the higher theflow rate the more rapid the evolution of the detonation wave. Hence,one exemplary embodiment uses a high flow rate. For a given sparkenergy, a certain flow rate defines the practical upper limit of flowrate. In one embodiment, the tubing that feeds the detonation tube isbelow a critical radius to prevent the detonation progressing back tothe fuel supply. For example, one embodiment use ¼″ diameter tubing toprevent such flashback and yet presents a low resistance to gas flow.For example, a 1″ long detonator having a ¼″ diameter bore hole canachieve detonation using a 1 joule spark within a MAPP gas-air mixtureflowing at 50 liters/minute.

Also shown in FIG. 2A is an optional secondary fuel-oxidant mixturesupply 105′. One or more secondary fuel-oxidant mixture supplies 105′can be used to speed up the filling of a large detonation tube (or tubecombination). With one approach, one or more secondary fuel-oxidantmixture supplies 105′ are used to speed up filling of a detonation tube100 in parallel with the (primary) fuel-oxidant mixture supply 105 suchthat detonator 114 can ignite the flowing fuel-oxidant mixture at adesired flow rate. With another approach, fuel-oxidant mixture supply105 may supply the detonation tube at a first higher rate and thenchange to a second rate prior to the flowing fuel-oxidant mixture beingignited. In still another approach, secondary fuel-oxidant mixturesupply 105′ supplies a different fuel-oxidant mixture 106′ (not shown inFIG. 2A) into detonation tube 100 than the fuel-oxidant mixture 106supplied by fuel-oxidant mixture supply 105 into detonator 114.

For certain fuels it may be necessary to heat the fuel-oxidant mixturein order to achieve detonation. Depending on the rate at which thedetonation tube is fired, it may be necessary to cool the detonationtube. Under one preferred embodiment of the invention, fuel supply 105(and/or 105′) comprises at least one heat exchange apparatus (not shown)in contact with the detonation tube that serves to transfer heat fromthe detonation tube to the fuel-oxidant mixture. A heat exchangeapparatus can take any of various well known forms such as small tubingthat spirals around the detonation tube from one end to the other wherethe tightness of the spiral may be constant or may vary over the lengthof the detonation tube. Another exemplary heat exchanger approach is forthe detonation tube to be encompassed by a containment vessel such thatfuel-oxidant mixture within the containment vessel that is in contactwith the detonation tube absorbs heat from the detonation tube.Alternatively, a heat exchanger apparatus may be used that isindependent of fuel supply 105 in which case some substance other thanthe fuel-oxidant mixture, for example a liquid such as water or silicon,can be used to absorb heat from the detonation tube. Alternatively,another source of heat may be used to heat the fuel-oxidant mixture.Generally, various well known techniques can be used to cool thedetonation tube and/or to heat the fuel-oxidant mixture includingmethods that transfer heat from the detonation tube to the fuel-oxidantmixture.

FIG. 2B depicts a first embodiment of the detonator of the presentinvention that functions by creating an electrical arc within a streamof a detonatable gas mixture. As shown in FIG. 2B, a gas mixture 106 ofa combustible gas and oxidizer in the correct detonable ratio is passedinto a detonation tube 100 via fill point 208 of detonator 114. When thetube is substantially full, high voltage wire 108 is triggered at highvoltage trigger input 214 to cause a spark 212 to occur across barewires 210 and to pass through the gas mixture 106 flowing into thedetonation tube 100 to initiate detonation of the gas in the detonationtube 100. Triggering of high voltage trigger is controlled by timingcontrol mechanism 216.

FIG. 2C depicts a second embodiment of the detonator of the presentinvention that also functions by creating an electrical arc within astream of a detonatable gas mixture. As shown in FIG. 2C, a gas mixture106 of a combustible gas and oxidizer in the correct detonable ratio ispassed into a detonation tube 100 via fill point 208 of detonator 114.When the tube is substantially full, high voltage wire 108 is triggeredat high voltage trigger input 214 to cause a spark 212 to occur acrossbare wires 210 and to pass through the gas mixture 106 flowing into thedetonation tube 100 to initiate detonation of the gas in the detonationtube 100. In this variation the spark is initiated within detonator 114and then it is quickly swept along the two diverging conductors into thedetonation tube 100 by the flowing gas, the length of the sparkincreasing as it travels into the detonation tube 100. When a spark isinitiated in a small gap it creates a stable low impedance zone that iscapable of conducting the same voltage electricity across a much largergap. Alternatively, the wires 210 may be parallel but bent slightlycloser together to ensure that the spark starts inside detonator 114.FIGS. 3A and 3B provide end and side views of an exemplary embodiment ofthe overpressure wave generator 11 of the present invention. As shown inFIGS. 3A and 3B, detonator 114 comprises insulating cylinder 302surrounding detonator tube 304. Electrodes 306 are inserted from thesides of insulating cylinder 302 and are connected to high voltage wire108. The detonator tube 304 is connected to fuel-oxidant mixture supply105 (shown in FIG. 3B) at fill point 208 and to detonation tube 100 atits opposite end. As shown in FIG. 3B, a gas mixture 106 is passed intothe detonation tube 304 and then into detonation tube 100 via fill point208 of detonator 114. When detonation tube 100 is essentially full, highvoltage wire 108 is triggered to cause a spark 212 to occur acrosselectrodes 306 and to pass through the gas mixture 106 flowing intodetonator tube 304 to initiate detonation of the gas in detonation tube100. Also shown in FIG. 3B is a Shchelkin spiral 308 just inside theclosed end of detonation tube 100. The Shchelkin spiral 308 is wellknown in the art as a deflagration-to-detonation transition (DDT)enhancement device. In one exemplary embodiment of the invention theShchelkin spiral 308 has 10 turns, is 7″ long, and is constructed using#4 copper wire that is tightly wound against the inside of thedetonation tube 100 at its base (closed end).

Overpressure Wave Magnitude Control

Generally, the length and inside diameter of a detonation tube can beselected to achieve a desired maximum generated overpressure wavemagnitude at a maximum selected flow rate of a selected flowingfuel-oxidant mixture, and the flow rate can be reduced to lower themagnitude of the generated overpressure wave. If required, increasinglylarger tubes can be used to amplify the detonation pulse initiallyproduced in a smaller detonation tube. Each one or a plurality of thetubes can be made of one or a combination of materials and allows,including PVC or a variety of different compounds, metals, or evenconcrete to achieve a desired result. In one exemplary embodiment thedetonation tube is made of titanium. In an exemplary embodiment, thedetonator within which the spark is introduced has a small diameter,e.g. approximately ¼″ diameter. This assembly is aligned to the base ofa second larger detonation tube so that the gas contained within it isdetonated. This second detonation tube may then be aligned to the baseof a successively larger diameter tube to initiate detonation of the gasmixture within. In this way, very large diameter detonation tubedetonations may be initiated with precise timing accuracy. The use oftubes having increasingly larger diameters is shown in FIG. 4 whichillustrates a graduating detonation tube combination 400 comprisingincreasingly larger detonation tubes that amplify a detonation pulse. Adetonation pulse produced in an initial detonation tube 100A travelsthrough detonation tubes 100B and 100C having larger diameters.Generally, as the detonation of the gas mixture transitions from adetonation tube having a smaller diameter to a detonation tube having alarger diameter the size of the pulse is amplified. In accordance withthe invention one or more detonation tubes having different diameterscan be combined into a graduating detonation tube combination 400. Inthe exemplary embodiment described above, the detonation tube (and thedetonator tube) was assumed to be a tube having a circumference thatdoes not vary over the length of the tube. As an alternative, adetonation tube (or detonator tube) may begin with a small diameter andgradually grow larger in order to have a similar effect of amplifyingthe pulse as described for FIG. 4. One exemplary approach is shown inFIG. 5 which depicts a side view of a detonation tube 100 having agradually enlarging diameter. The diameter of a detonation tube becominglarger and larger causes the pulse to be amplified as it travels thelength of the tube in a manner similar to the graduated tube techniqueof FIG. 4. As shown, detonation tube 100 has a first diameter 502 at oneend that is smaller than second diameter 504 at the other end. Multipletubes having enlarging diameters can also be combined. Another variationof the detonation tube is to use a compressor/expander technique wherethe circumference of the tube tapers to a smaller circumference tocompress the gas and then expands to a larger circumference to expandthe gas. This approach is shown in FIG. 6 which depicts a side view ofdetonation tube 100 based on the compressor/expander technique that hasa first diameter 602 at one end, a second diameter 603 at the other endand a third diameter 604 between the two ends of the detonation tube100. The first diameter 602 may or may not equal second diameter 603depending on desired compression/expansion characteristics.

Detonation Tube Arrays

Detonation tubes can be grouped into arrays in various ways to produce acombined pulse when triggered simultaneously. FIGS. 7A-7D depictexamples of how detonation tubes can be combined. FIG. 7A depicts adetonation tube array 702 comprising a first detonation tube alongside asecond detonation tube. FIG. 7B depicts a detonation tube array 704comprising four detonation tube combinations arranged such that thelarger detonations tubes of the detonation tube combinations are incontact with each other. FIG. 7C depicts detonation tube array 706comprising three enlarging diameter detonation tubes. FIG. 7D depictsdetonation tube array 708 comprising seven detonation tubes arranged toresemble a hexagonal structure. FIG. 7E depicts detonation tube array710 comprising twelve detonation tubes arranged in a circular manner.

Alternatively, the detonation tubes that make up such detonation tubegroups or arrays can also be triggered at different times. Under onearrangement, detonation tubes are ignited using a timing sequence thatcauses them to detonate in succession such that a given detonation tubeis being filled with its fuel-oxidant mixture while other detonationtubes are in various states of generating an overpressure wave. Withthis approach, the igniting and filling of the detonation tubes could betimed such that overpressure waves are being generated by the apparatusat such a high rate that it would appear to be continuous detonation.

As shown in FIG. 8, a group of smaller tubes can be connected to alarger tube such that their combined pulses produce a large pulse thatcontinues to detonate in the larger tube. FIG. 8 depicts a side view of3 smaller detonation tubes 100A having a first diameter connected to alarger detonation tube 1008 having a second larger diameter to amplify acombined pulse.

Generally, any of various possible combinations of graduated tubes,tubes of gradually increasing circumferences, tube arrays, groups ofsmaller tubes connected to larger tubes, and tubes employing thecompressor/expander technique can be used in accordance with this aspectof the invention to generate overpressure waves that meet specificapplication requirements. All such combinations require balancing theenergy potential created due to an expansion of a pipe circumferencewith the cooling caused by expansion of the gases as the tubecircumference increases.

Coherent Focusing and Steering of Overpressure Waves

As described previously, the detonator of this aspect of the presentinvention has low uncertainty of time between the electric arc triggerand the subsequent emission of the sound pulse from the tube. Thedetonator also provides for repeatable precision control of themagnitude of the generated sound pulses. This low uncertainty, orjitter, and precision magnitude control enables the coherent focusingand steering of the overpressure waves generated by an array ofdetonation tubes. As such, the detonator can be used to generatesteerable, focusable, high peak pulse power overpressure waves.

FIG. 9 illustrates how the timing of the firing of individual tubesfocuses the power of the generated overpressure waves at a single pointin the far field. Tubes further away are triggered earlier to compensatefor the greater amount of time required to travel a greater distancewhich causes all the pulses to arrive at the same point in space at thesame time. FIG. 9 depicts an array 900 of detonation tubes 100A-100Ethat are ignited (or fired) with controlled timing as controlled bytiming control mechanism 216 such that the sound pulses they generatearrive at point in space 902 at the same time. The sound pulses 906produced by detonation tubes 100A-100E travel along direct paths904A-904E, respectively. As such, they are fired in sequence 100E-100Awith appropriate delays between firings to account for different timesof travel required to travel the different direct paths so that thesound pulses 906 arrive at point in space 902 at the same time toproduce combined sound pulse 908.

Individual detonation tubes or groups of tubes can be arranged in asparse array. FIG. 10 depicts an array of individual detonation tubesarranged in a sparse array where the timing of the detonations in thevarious tubes is controlled so as to steer the overpressure waves suchthat they combine at a desired location. FIG. 11 similarly depicts anarray of groups of tubes arranged in a sparse array where the tubes of agiven group are detonated at the same time but the detonation timing ofthe various groups is varied so as to steer the overpressure waves sothey combine at a desired location.

Referring to FIG. 10, detonation tubes 100A-100D are fired in reversesequence with precise timing as controlled by timing control mechanism216 such that sound pulses travel direct paths 904A-904D and combine atpoint in space 902. Referring to FIG. 11, detonation tube groups1100A-1100D are fired in reverse sequence as controlled by timingcontrol mechanism 216 such that sound pulses travel direct paths904A-904D and combine at point in space 902.

The timing control mechanism 216 used in sparse array embodiments maycomprise a single timing control mechanism in communication with each ofthe overpressure wave generators making up the array via a wired orwireless network. Alternatively, each of the overpressure wavegenerators may have its own timing control mechanism whereby the timingcontrol mechanisms have been synchronized by some means.

Theory of Operation of Detonation Tube Arrays

Generally, when an array of detonation tubes is triggered with precisetiming a pressure wave is created that propagates as a narrow beam in adirection mandated by the timing. In this way its operation is analogousto a phased array antenna commonly used in radar systems. Since thetiming is determined electrically the beam direction can be redirectedfrom one pulse to the next. Systems can be designed that operate atdifferent rates, for example 10, 20, 50 or 100 pulses per second, andeach pulse can be aimed in a unique direction. The only limitation torepetition rate is the speed with which the tubes can be refilled. At asonic refill rate it would take about five milliseconds to refill a tubefive feet long. Since it also takes a pulse five milliseconds to exitonce detonated, the limiting repetition rate is 100 Hz.

Since each element of the array emits its own coherent energy, in thefar field the amplitude of the wave approaches the square of theintensity of each individual tube. The instantaneous over pressures thatcan be directed in this way therefore may approach high levels. As such,the system possesses a large overhead dynamic range that can be used toreach a long range or propagate through small apertures in structuressuch as hard targets.

The structure behind the small aperture can be resonated by applicationof the pulses at just the right time intervals, as determined by a probelaser used to measure the Doppler shift of particles at the opening. Thenatural frequency of the structure can thereby be determined andthereafter the laser is used in closed loop mode to control the timingof the system to produce maximum effect. The instantaneous pressuresinside such a hard target can be quite large since the acoustic Q ishigh. For example, for a Q of only 10 the peak pressure could approach1000 psi.

Groups of detonation tubes can be treated as sub-arrays within a largerarray. FIG. 12 illustrates an exemplary embodiment of 32 hexagonalsub-arrays 1202 of 7 detonation tubes each efficiently packed into anarray 1200 having a total of 224 3″ diameter detonation tubes in a6.2′×2.5′ format. The far field intensity of this system can be over50,000 times the intensity of one such 3″ detonation tube.

Timing of the firing of the array elements of this embodiment isstraightforward. The waveform is about one millisecond long and theconstraint for coherence is ¼ of its wavelength or less. The timingsubsystem therefore will need a resolution and accuracy of 200microseconds or less. This level of timing accuracy can be accomplishedwith programmable counter-timers such as Intel's 8254 PCA that providesthree channels of timing per chip, at a resolution of 0.1 microsecond.

In one embodiment, each element in a steerable array needs to have itsenergy spread over the entire area of steerability, for example, with anaperture that has under ½ wavelength. For a one millisecond waveform theaperture is about six inches. In the exemplary embodiment shown in FIG.12, the hexagonal sub-array bundles are nine inches across so they willnot allow steering over a full half hemisphere but grouping the tubesinto the hexagonal bundles that are fired as a group reduces thehardware requirements allowing thirty two programmable timing channelsare used to focus and steer the array. As such, all timing needs can bemet with only eleven 8254's. A PCI board made by SuperLogics containsfour 8254's giving twelve programmable counter-timers so three moduleswould suffice. In another embodiment, the tubes of each buddle in FIG.12 could be spaced apart sufficiently to enable steering over a fullhalf hemisphere and the firing of all the tubes could be independent,without grouping.

The focal spot of the array is a function of the wavelength and the sizeof the array. Near the array face the focal spot comprises anapproximate circle one wavelength, i.e. one foot in diameter. At greaterdistances the spot will gradually spread out in an oval shape with itslarge diameter in the direction of the small diameter of the array. Thatis, the oval becomes vertical for the horizontal array depicted in FIG.12. The shape of the focal spot can be easily modeled using the waveequation when it is operated in the linear regime up to about half anatmosphere or 7 psi. However when the instantaneous pressure in thewaveform approaches an atmosphere it will be non-linear and thecalculation differs.

Measurements of the pressure output of the array can be made with a wideband acoustic sensor. They typically have a bandwidth of 10-20,000 Hzand an accuracy of 1 dB or so. Measurements made at a distance of thirtyfeet or more in the far field of the array give accuracies sufficient toextrapolate characteristics at any range. The calibrated output of suchan instrument is acoustic sound pressure level which has a directrelationship to pressure, i.e.

${L_{p}({dBSPL})} = {{10 \cdot \log_{10}}{\frac{p}{p_{0}}.}}$

For example, 180 dBSPL is equivalent to a pressure of 20,000 Pa or about3 psi. The instantaneous sound intensity associated with this level is1,000,000 W/m².

A consequence of the general wave equation for linear media is that whenwaves superimpose their amplitudes add. For electromagnetic waves thismeans that if two identical waves arrive at a point in space at the sametime and phase they will produce double the potential, or voltage of asingle wave.

The result is similar in the case of acoustic waves but in this case thepotential is pressure rather than voltage.p=√{square root over (p ₁ ² +p ₂ ²+2p ₁ p ₂ cos(θ₁−θ₂))}N/m ²Note that since the phases are equal the cosine is equal to 1 and thevalue of the pressure is equal to twice the pressure of a single source.This relation applies for the addition of N sources=N*p.

Doubling the pressure of an acoustic waveform quadruples its power sincepower is proportional to the square of its pressure, namely, when twoidentical acoustic waveforms arrive at the same point in space at thesame time and phase their power will quadruple.

In analogy to electromagnetic waves the power, or acoustic intensity, ofa waveform is proportional to the square of its pressure.

$I = {\frac{p^{2}}{\rho\; c}\mspace{14mu}{Watts}\text{/}m^{2}}$Where the denominator is the value of the acoustic impedance of themedium, in this case air.

Therefore, generally the free-space, far-field power in the main lobe ofthe overpressure waveform can be calculated as N² of the pressure of asingle detonation tube. However, when it is operated near the ground,advantage can also be taken of the additive effect of the ground wave.When the wave from the ground and the free-space waveforms converge on atarget the pressures of both waveforms again add and quadruple the poweragain.

Beam steering is accomplished by adjusting the timing of the individualelements such that the closer ones are delayed just enough for the wavesfrom the further part of the array to catch up. In a given steeringdirection therefore all of the waves will arrive at the same time andsatisfy the N² power criterion. This is analogous to a phased arrayantenna but since the acoustic waveform is transient rather thancontinuous wave, time delay is substituted for phase.

Applications of the Overpressure Wave Generator of the Present Invention

Applications of the overpressure wave generator of the present inventioninclude but are not limited to explosives emulation for trainingpurposes, explosives barrier testing, demolition of mines/buildings,crowd control, border defense, animal/bird/insect control, prisonercontrol, structural strength/integrity testing, providing rotary motionto a windmill or a turbine, use as a thrust source for rocket-likepropulsion, dirt/sand/snow/ice removal for roads/runways/airplanes/etc,fruit/vegetable/grain/etc. harvesting from trees/bushes/plants andcomparable agriculture applications, industrial cleaning (e.g., smokestacks/precipitators), object forming (e.g., a compliant press/moldingprocess), fire suppression, and, in general, most any areadenial/security application.

Using the Recoil Force of an Overpressure Wave for Seismic Exploration

The overpressure wave generator of the present invention described abovecan be augmented so as to harness its recoil force for seismicexploration purposes. Recoil force is the backward kick or forceproduced by the detonation of overpressure waves. This force is equal tothe derivative of the backward momentum resulting from detonation ofoverpressure waves. In one embodiment of the seismic exploration systemin accordance with the present invention, as shown in FIG. 13, seismicexploration system 1300 includes an overpressure wave generator 11, acoupling component 1312, a stabilizing mechanism 1313 for controllingthe movement of the overpressure wave generator, a controller 1314 forcontrolling the operation of the overpressure wave generator 11, an echodetector 1316, a data recorder 1318, an image processor 1320, and adisplay device 1322. It should be understood that while the foregoingelements of the system 1300 are identified separately, these elements donot necessarily have to be physically separated. Some elements can beconfigured to reside on the same machine, for example, the controller1314, the data recorder 1318, and the image processor 1320 can all beparts of a single computer. The system 1300 may optionally include amuffling apparatus 1324 which includes vent 1328 used to providedilution gas (e.g., air) used to prevent detonation from continuing intothe muffling apparatus 1324. Alternatively, the seismic explorationsystem can be operated without using coupling component 1312, in whichcase overpressure wave generator 11 will be directly in contact with theground 1330.

Exemplary overpressure wave generator 11 of system 1300 may include anyof the variations described above. It includes an electrical (or laser)source for producing a spark, a detonation tube, a gas mixture sourcethat provides the flowing gas into the detonation tube, and a detonator.For the purposes of the description below, the overpressure wavegenerator can alternatively be a group of detonation tubes that aredetonated simultaneously so as to produce a combined overpressure wave.

The overpressure wave generator is detonated to generate an overpressurewave, which is optionally muffled by muffler 1324. The generation of theoverpressure wave causes a corresponding recoil force which couplingcomponent 1312 couples to a target media such as the ground, ice, orwater to produce a conducted acoustic wave. Stabilizing mechanism 1313provides stability to the movement of the overpressure wave generator 11essentially allowing only up and down movement. Coupling component 1312may comprise a spring or may comprise rubber or some comparable compoundhaving desired spring-like and damping characteristics, such as opposingpolarity magnets. Coupling component also comprises impedance transitiondevice 1326 having a desired shape which directly contacts the ground1330 to impart the conducted acoustic wave. Impedance transition device1326 can have any of various types of shapes including having a singlesharp point, multiple sharp points, a flat plate-like shape that may besquare, rectangular, circular, or any other desired shape. In anexemplary embodiment, the impedance transition device 1326 has a flatround shape. If the target media is water, the coupling component maycomprise a diaphragm that is in contact with the water. If the targetmedia is solid such as the ground or ice, the overpressure wavegenerator may alternatively be placed directly in contact with thetarget media such that its recoil force will be directly coupled to thetarget media.

Under one embodiment of the present invention, multiple conductedacoustic waves are delivered to the ground in a sequence timed inaccordance with a timing code that has desirable correlation properties.Coding of the pulses permits pulses to be emitted at a higher rate thancould be accomplished by waiting for all echoes to subside before newpulses are generated. Such coding thereby increases the power of theemitted signal and reduces the time needed to acquire an image of agiven signal-to-noise ratio. For example, a Barker code has desirableautocorrelation properties. Any of various coding techniques thatprovide desirable correlation properties that are well known in the artof radar and communications can be used.

As previously mentioned, the overpressure wave is generated by thecontrolled and directed explosion of a detonable gaseous or dispersedfuel-air or fuel-oxygen mixture. Any of a number of flammable fuels canbe used including ethane, methane, propane, hydrogen, butane, alcohol,acetylene, MAPP gas, gasoline, and aviation fuel. The use of suchflammable fuels have significant advantages over solid and/or liquidexplosives, since they are easily obtainable from various sources andare relatively low in cost. The overpressure wave is generated inaccordance with detonation parameters such as the mass ratio of thefuel-oxidant mixture, a timing code, etc.

Furthermore, the explosion of a flammable fuel produces more accurateresults. Maximum energy is imparted to the ground per unit of timeresulting in a clearer picture. The improved clarity is attributed tothe reduction of non-linearity effects. Non-linearity effects aresubstantially reduced because the coupling component 1312 does notcompress the earth thereby producing mostly linear signals. In addition,a series of smaller explosions can be set off over a period of time, andthe resulting received signals can be integrated to obtain any desireddegree of resolution and any desired depth can be reached by extendingthe detection period.

The controller 1314 is used to control the operation of the overpressurewave generator 11. The controller 1314 can be a portable computer orworkstation which is programmed to generate the desired time-codedtiming sequence upon which the overpressure wave generator 11 istriggered.

The echo detector 1316 can be made up of an array of sensors orgeophones. This array of geophones constitutes a synthetic aperturearray which is analogous to synthetic aperture array radar. Thissynthetic aperture array allows for the capture of highly focused, clearimage data from the subsurface in multiple focal lengths and in realtime without moving or modifying the array configuration. This allowsdata taken from an array of non-directional sensors to be focused at anypoint in the ground via post-processing. Such processing is thegeophysical analogy to synthetic aperture array processing, meaning thatthe data from the individual geophones can be combined coherently to bethe equivalent of a much larger focusable geophone. Using this syntheticaperture array, data collection is done with fewer geophones than bothexplosives and vibration couplers. Furthermore, the array of geophonescan be distributed randomly and are not required to be arranged in aconventional grid array.

The data or echoes captured by the echo detector 1316 are stored in thedata recorder 1318 for subsequent processing. Various types of storagedevices commonly known in the art can be used as the data recorder 1318.Similarly, conventional devices commonly known in the art can be used asthe image processor 1320 and the display device 1322.

FIG. 14 illustrates the logical steps taken during the operation of thesystem 1300 in accordance with the present invention. At step 1400,overpressure wave generator 11 and coupling component 1312 direct asequence of time coded conducted acoustic waves into the subsurfacewhere they are reflected and scattered by subsurface variations inphysical properties.

At step 1420, the echoes or waves returning to the surface are detectedby the echo detector 1316, i.e., the geophones. The geophones record thetime histories of ground motion over a few seconds. The amplitudes,frequencies, and phases of these trace recordings are affected byvarious physical properties of the subsurface such as elastic constants,geometry, dimensions, inelasticity and anisotropy.

At step 1440, the data recorder 1318 stores the response of the earth asdetected by the geophones. The data recorder 1318 communicates with thegeophones via an analog-to-digital converter and a multiplexer, andrecords and stores the data in one of several optional storage devicesfor subsequent processing and display.

At step 1460, the recorded data can be processed by the image processor1320 in accordance with various well-known imaging algorithms and theresults can then be displayed through the display device 1322.

The conventional presentation of seismic data is to plot a series ofreturn amplitude vs. time waveforms on the vertical axis (a waveformplot). The “wiggles” are reflections due to inhomogenities of physicalproperties. The layout of the geophone array and the subsequent dataprocessing to form an image from a synthetic aperture array is analogousto a synthetic aperture radar array. In analogy to optical lens systems,a fixed focal length antenna array would not remain in focus through thewhole depth of field required if the system must image from near thesurface to hundreds of feet below the surface. Thus, the antenna wouldneed to be both large to cover a reasonable area of ground and alsofocusable in real time.

Since off axis reflections are received at successively greater delaysat the antenna, they create a “point scatterer” which traces a curve inthe resulting image. This curve is calculable, and can be removed inpost processing. This allows data taken from an array of non-directionalantennas to be focused at any point in the ground via post processing.Such synthetic aperture array processing enables the data from theindividual antennas to be combined coherently so as to be the equivalentof a much larger focusable antenna.

The primary data wavefront curves are generated virtually in real timeand can be interpreted by an experienced geophysicist. Spatial locationsand 3-D imagery can be generated by using standard tomographic imageprocessing. Higher resolution subsurface discrimination can be achievedthrough the combination of successive wavefront curves over time.

The system 1300 has the capability to provide a quick look at the datain the field in real time. This capability can be useful to guide thedirection of subsurface imaging efforts based on what is found in thefield and ensure that the data taken to be analyzed are of sufficientfidelity and signal-to-noise ratio for maximum utility.

Alternatively, multiple systems 1300 can be arranged in a sparse arrayand timing control methods used to steer their conducted acoustic wavessuch that they combine at a desired location within the ground. Suchsteering is essentially done in the same manner similar as overpressurewaves are steered, as described in relation to FIGS. 9-11 except it isaccomplished with multiple time-controlled conducted acoustic waves.FIG. 15 illustrates multiple systems 1300A-1300C being controlled suchthat the conducted acoustic waves travel through the ground via directpaths 904A-904C such that they combine at a point under ground 1502. Theability to focus and steer the conducted acoustic waves of the presentinvention enables precision imaging of features deep within the groundsuch as oil formation 1504. If the target media is water, beam steeringcan be used to chart the bottom of a water body.

FIG. 16 depicts an exemplary circular array pattern that can be used forbeam steering purposes. Such patterns can be placed with larger arraysto provide a scalable architecture used to explore large areas. In FIG.16, seismic systems 1300 are arrayed in circular sub-arrays 1602 whichmay themselves become part of a larger circular sub-array 1604, and soforth, to cover very large areas. Generally, the seismic systems 1300 ofthe present invention can be placed in any desirable and practicalarrangement of known locations and used in accordance with the presentinvention.

Other Applications Enabled Using the Recoil Force of an OverpressureWave

Other applications enabled using the recoil force of the overpressurewave of the present invention include but are not limited to powering anengine or a pump, driving fence posts/piles into the ground, use as atamping device (e.g., to compact dirt), use as a forced entry device(like a battering ram), imaging a water body bottom, and use tocrush/deform objects/stamp metal/etc.

Use of the Overpressure Wave Generator as a Shear Wave Generator forSeismic Exploration

In a third embodiment of the invention, overpressure wave generator 11is used as a shear wave generator for seismic exploration purposes. Ashear wave, also known as S-wave, secondary wave or an elastic S-wave,is one of the two main types of elastic body waves, no named because,unlike surface waves, shear waves move through the body of an object.Seismic exploration system 1700 in accordance with the present inventionis shown in FIG. 17A. Seismic exploration system 1700 includes anoverpressure wave generator 11, a plane defining mechanism 1702, acoupling component 1312, a stabilizing mechanism 1313 for controllingthe movement of the overpressure wave generator, a controller 1314 forcontrolling the operation of the overpressure wave generator 11, an echodetector 1316, a data recorder 1318, an image processor 1320, and adisplay device 1322. It should be understood that while the foregoingelements of the system 1300 are identified separately, these elements donot necessarily have to be physically separated. Some elements can beconfigured to reside on the same machine, for example, the controller1314, the data recorder 1318, and the image processor 1320 can all beparts of a single computer. The system 1700 may optionally include amuffling apparatus 1324 which includes vent 1328 used to providedilution gas (e.g., air) used to prevent detonation from continuing intothe muffling apparatus 1324. Alternatively, the seismic explorationsystem 17000 can be operated without using coupling component 1312, inwhich case overpressure wave generator 11 and plane defining mechanism1311 will be directly in contact with the ground 1330.

The overpressure wave generator 11 of system 1700 may include any of thevariations described above. It includes an electrical (or laser) sourcefor producing a spark, a detonation tube, a gas mixture source thatprovides the flowing gas into the detonation tube, and a detonator. Forthe purposes of the description below, the overpressure wave generatorcan alternatively be a group of detonation tubes that are detonatedsimultaneously so as to produce a combined overpressure wave.

The overpressure wave generator 11 is detonated to generate anoverpressure wave. The generation of the overpressure wave causes acorresponding recoil force parallel to the ground causing plane definingmechanism 1311 to move across coupling component 1312. Plane definingmechanism 1311 is in contact with 1312 to define a plane across itperpendicular to the movement of overpressure wave generator 11.Coupling component 1312 couples the shear wave to the target media toproduce a conducted acoustic wave. Stabilizing mechanism 1313 providesstability to the movement of the overpressure wave generator 11essentially allowing only side to side movement. Coupling component 1312may comprise a spring or may comprise rubber or some comparable compoundhaving desired spring-like and damping characteristics.

FIG. 17B depicts a plane shear wave propagating from right to left as isproduced given the orientation of the system 1700. Generally, the planeshear wave produced by system 1700 has the same directionality as therecoil force of the overpressure wave generator 11.

FIG. 18A depicts a plan view of a spherical shear wave generator 1800 inaccordance with one embodiment of the present invention. As shown, twoplane shear wave systems 1700A and 1700B are oriented such that theplane shear waves they produce are in opposite directions causing themto produce a spherical shear wave.

FIG. 18B depicts a spherical shear wave moving in a counterclockwisedirection. Generally, the spherical shear wave produced by system 1800is either clockwise or counterclockwise depending on the orientation ofthe systems 1700A and 1700B to each other.

FIG. 18C depicts a plan view of a spherical shear wave generator 1800 inaccordance with another embodiment of the present invention. As shown,four plane shear wave systems 1700A-1700D are oriented such that theplane shear waves they produce are in opposite directions causing themto produce a spherical shear wave.

FIG. 18D depicts a plan view of a spherical shear wave generator 1800 inaccordance with still another embodiment of the present invention. Asshown, six plane shear wave systems 1700A-1700F are oriented such thatthe plane shear waves they produce are in opposite directions causingthem to produce a spherical shear wave.

The various array techniques, coding techniques, etc. described inaccordance with the second embodiment of the invention are alsoapplicable with this third embodiment. As such, this embodiment also hasthe ability to focus and steer the conducted acoustic waves that enablesprecision imaging of features deep within the ground such as oilformation 1504. Similarly, this embodiment has the ability to image awater body bottom.

The improved seismic exploration system described herein was provided asan example of the types of applications that are enabled by the presentinvention. While particular embodiments and several exemplaryapplications (or implementations) of the invention have been described,it will be understood, however, that the invention is not limitedthereto, since modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. It is, therefore,contemplated by the appended claims to cover any such modifications thatincorporate those features or those improvements which embody the spiritand scope of the present invention.

1. A method for generating a conducted acoustic wave, comprising thesteps of: causing at least one detonation within at least one detonationtube having an open end to generate at least one overpressure wave; andcoupling a recoil force of said at least one overpressure wave to atarget media to generate at least one said conducted acoustic wave. 2.The method of claim 1, wherein said open end of said at least onedetonation tube is oriented to direct said at least one overpressurewave perpendicular to and away from said target media.
 3. The method ofclaim 1, wherein said open end of said at least one detonation tube isoriented to direct said at least one overpressure wave parallel to saidtarget media.
 4. The method of claim 3, wherein said recoil forcecorresponds to one of a plane shear wave or a spherical shear wave. 5.The method of claim 1, wherein said target media is at least one ofground, ice, or water.
 6. The method of claim 1, wherein each of said atleast one overpressure waves is generated by controlling, in accordancewith detonation parameters, the detonation of a fuel-oxidant mixtureflowing within each of said at least one detonation tube.
 7. The methodof claim 6, wherein said detonation parameters comprises a timing code.8. The method of claim 7, wherein said timing code is a Barker code. 9.The method of claim 1, further comprising the step of: muffling thesound of said at least one overpressure wave.
 10. The method of claim 1,further comprising the step of: steering a plurality of coupled acousticwaves of said at least one coupled acoustic wave to a location ofinterest within said target media by controlling the relative timing ofthe generation a plurality of overpressure waves of said at least oneoverpressure wave.
 11. A system for generating a conducted acousticwave, comprising: at least one detonation tube having an open end forgenerating at least one overpressure wave; and a coupling component forcoupling a recoil force of said at least one overpressure wave to atarget media to generate at least one said conducted acoustic wave. 12.The system of claim 11, further comprising a stabilizing mechanism thatprovides stability to the movement of the at least one detonation tube.13. The system of claim 12, wherein said open end of said at least onedetonation tube is oriented to direct said at least one overpressurewave perpendicular to and away from said target media and saidstabilizing mechanism allows only up and down movement.
 14. The systemof claim 12, wherein said open end of said at least one detonation tubeis oriented to direct said at least one overpressure wave parallel tosaid target media and said stabilizing mechanism allows only side toside movement.
 15. The system of claim 11, wherein said target media isat least one of ground, ice, or water.
 16. The system of claim 11,wherein each of said at least one overpressure waves is generated bycontrolling, in accordance with detonation parameters, the detonation ofa fuel-oxidant mixture flowing within each of said at least onedetonation tube.
 17. The system of claim 16, wherein said detonationparameters comprises a timing code.
 18. The system of claim 17, whereinsaid timing code is a Barker code.
 19. The system of claim 11, furthercomprising: a muffler associated with said at least one detonation tube.20. A system for generating and directing conducted acoustic waves,comprising: a plurality of overpressure wave generators positioned in asparse array, each of said plurality of overpressure wave generatorscomprising at least one detonation tube having an open end and beingused to generate a plurality of overpressure waves, each of saidplurality of overpressure waves having a recoil force; and a pluralityof coupling components for coupling said recoil forces of said pluralityof overpressure waves to a target media to generate said conductedacoustic waves, said conducted acoustic waves being directed to alocation of interest within said target media based upon the relativetiming of the generation of said plurality of overpressure waves.